Draft booster system for a wall furnace



July 30, 1968 R. R. COOPER DRAFT BOOSTER SYSTEM FOR A WALL FURNACE Filed March 23, 1967 2 Sheets-Sheet 1 y 1968 R. R. COOPER 3,394,696

DRAFT BOOSTER SYSTEM FOR A WALL FURNACE Filed March 23, 1967 2 Sheets-Sheet 2 I v BLOWER I 1 MOTOR Q2 1 I I :57 3 VOLTAGE CONVERTER QT 7% L52 V 60 was 51-01% /.50 MA w ACSOURCE BATTERY 230 jfliOYf 170667 5 1. Q 796). qr, QZZM 25a MWW United States Patent 3,394,696 DRAFT BOOSTER SYSTEM FOR A WALL FURNACE Robert R. Cooper, Wichita, Kans., assignor to The Coleman Company, Inc., Wichita, Kans., a corporation of Kansas Filed Mar. 23, 1967, Ser. No. 625,547 6 Claims. (Cl. 126-116) ABSTRACT OF THE DISCLOSURE A draft booster for a wall furnace or space heater including a motor-driven booster fan in the combustion air conduit adjacent the fresh air intake, a flap or sail pendantly mounted in the conduit between the fresh air intake and the booster fan, and a snap switch having an elongated extension to its moveable contact which engages the flap. When the flap moves responsive to the movement of combustion air, the extension is pushed to close a circuit for energizing a solenoid controlling gas to the burner of the furnace. An input bafile structure prevents rain from entering the combustion air conduits.

Background The present invention relates to a small furnace; more particularly it relates to a system for forcing the combustion air through the furnace and for proving the flow of the forced combustion air before allowing the fuel to enter the burner.

Forced combustion air systems are not new; and they have been used particularly in cases in which installation of a balanced vent assembly was not feasible or where it is desired to augment the natural flow of combustion air under certain conditions.

Further, systems are known for proving the flow. of combustion air prior to energizing whatever means feeds the fuel to the burner. Such systems are responsive either to the feeding of electrical energy to the draft boosting fan or to the actual flow of air. However, none of the known systems could be adapted for the particular environment in which the instant invention must operate.

The draft booster of the instant invention is designed to force combustion air through a very small furnace which is adapted to be received in an external wall of a mobile home or trailer.

Typically, such a mobile home may be thirty feet long and a single space heater with convection heating alone is insufficient to properly heat the home. Hence, it is required that the heated air system also be a forced air system.

The receptacle in which the furnace is received in the exterior wall of the home is, of course, as small as is practicable; and the exterior faceplate of the furnace is preferably flush with the exterior wall of the trailer, or at least it must present no sharply protruding elements. Hence, the combustion air intake orifice, as well as the combustion air outlet orifice, are generally in a vertical plane, and the conduits leading to them are relatively small and as free from obstruction as possible. In addition, the flow of combustion air is not great, being of the order of fifteen cubic feet per minute. A problem arises in sensing the flow of air at such a low rate and sustaining a signal during continuous flow of the combustion air. Further, the combustion air conduits should be sheltered against rain.

Summary The present invention provides for an axially-driven rotary fan located in the combustion air conduit adjacent See the intake orifice and a pendantly hung flap or sail located between the fan and the intake orifice. The flap substantially covers the intake orifice and blocks the intake conduit. A snap switch is mounted in the conduit interior of the sail switch. The moveable contact of the snap switch is fitted with an extension defining a lever arm which extends to about the middle of and engages the rear of the flap. When the fan is energized to force air through the combustion conduits, the flap will be rotated slightly to trigger the snap switch which then energizes the main gas solenoid for feeding fuel to the burner.

Thus, even though a very small volume of combustion air is forced through the combustion conduits, there is nevertheless provided a very sensitive system for proving the flow of combustion air prior to feeding fuel to the burner. Vent and bafiie plates are provided at the combustion air intake and outlet to prevent rain from entering the combustion air conduits.

Other advantages and features of the present invention will be obvious to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing in which identical reference numerals will refer to like elements in the various views.

The drawing FIG. 1 is a side elevational view of the external mounting plate for a wall furnace illustrating the intake and outlet combustion air vents and the baffies for routing the combustion air;

FIG. 2 is a side sectional view of a furnace incorporating a forced combustion air system according to the present invention;

FIG. 3 is a detailed side view of the fan and air proving system of the furnace of FIG. 2; and

FIG. 4 is a block schematic diagram of the air proving system of the furnace of FIG. 2.

Detailed description Referring then to FIG. 1, an external wall of a mobile home or trailer is designated 10, and it defines an opening or receptacle for receiving a furnace, generally designated as 11. The furnace .11 slides into a duct boot, three sides of which are shown in FIG. 1 and identified by reference numerals 12, 13 and 14. The duct boot serves as a sealing receptacle between the forced, heated air outputs of the furnace and the distribution duct work of the trailer which is to be heated; and it does not form part of the instant invention, which has to do with the combustion air system.

An exterior mounting plate 15, covers the furnace 11 and seals its periphery with the opening or receptacle in the trailer wall 10.

Affixed to the mounting plate 15 are an upper vent and bafile plate 16 and a lower vent and baffle plate 17. The lower vent and baffle plate, which is partially cut away in FIG. 1, is identical to the upper vent and bafiie plate 16. Each of the vent and baffie plates 16 and 17 i a rectangular sheet metal plate elongated in the horizontal direction. Each plate contains a left-hand set of vents, a right-hand set of vents, and a solid center plate. These vents are identified respectively as 18 and 19 for the vent and baffie plate 16 and as 20 and 21 for vent and baffle plate 17. The vents 1821 are formed by simply cutting parallel, elongated horizontal sections of the outer surface of the- 4 plate on three sides. The tab defined by the three cuts is then inclined rearwardly about its horizontal lower boundary. Hence, a set of such tabs defines a vent which contains louvers inclined upwardly and rearwardly of the exterior surface of the plate.

The vents of the lower vent and bafiie plate 17 communicate with the combustion air intake, the periphery of which is identified by reference numeral 22 in FIG. 1. It can there be seen that the combustion air intake conduit is shielded by the solid center plate of the vent and baffle plate 17. Similarly, although not shown, the combustion air outlet is located directly behind the solid center plate of the upper vent and baffle plate 16.

The arrangement of vents and baffles described above advantageously nullifies any velocity component of a gust of wind directly into either the combustion air intake conduit or the combustion air outlet conduit by forcing air upward through the inclined louvers in the vents and behind the center portion of the plate. In addition, the solid center parts of the vent and baffle plates 16 and 17 prohibit rain from entering the combustion air conduits.

Turning now to FIG. 2, the heated, forced air system of the furnace conventionally comprises a squirrel cage blower 25, for drawing the cold air from the interior of the trailer and forcing it over a heat exchanger 26 in which there is situated a burner 27 for burning fuel controlled by a main gas solenoid 28 (shown in phantom). The cold air is heated upon contact with the heat exchanger 26 and circulated back through the trailer distribution duct work, which may include a horizontal duct 29 and a vertical duct 30.

The combustion air is drawn in through the louvers in the vent and bafile plate 17 into the inlet conduit 22 which narrows beneath the burner 27. The combustion air is then routed upward beyond the burner 27, where it is heated, over the interior walls of the heat exchanger 26, out through an upper combustion air outlet 31, and through the louvers in the upper vent and baflle plate 16.

The enlarged portion of the inlet conduit 22 defines a receptacle for receiving an integral module or frame 32 of generally square contour containing certain of the components of the air proving system.

In FIG. 3, the elements contained within the frame 32 are shown in detail. A vertical bracket 33 is mounted at its top and bottom to the frame 32 by means of bolts 34 and 35. A small electric motor, generally designated by reference numeral 36, is mounted on the plate 33 with its shaft 37 extending through the plate 33 and generally coaxial with the axis of the frame 32. A propeller fan blade 38 is secured to the shaft 37 by means of a collar 39 and bolt 39a.

Wires 40 represent the feed lines to the motor 36, and they are coupled to one terminal of a four-wire connector, identified by reference numeral 41. Use of the connector 41 facilitates replacement of the complete module.

A flap or sail 42 is pendantly hung at 43 and suspended from the top of the frame 32 immediately in front of the motor 36. The flap 42 conforms substantially to a vertical cross section of the inlet conduit defined by the frame 32., so that it will be forced rearward toward the motor 36 when combustion air flows through the intake orifice. A U-shaped trough 44 is fixed to the bottom of the frame 32 transverse of the direction of air flow and confining the lower portion of the flap 42. The trough 44 permits a slight forward motion and somewhat more rearward motion of the flap 42. Thus, the U-shaped trough 44 prevents the flap 42 from ever being forced out of the intake conduit in one direction and from moving so far rearward that it would permanently bend the lever arm of a snap switch which it pushes.

A snap switch 45 is mounted on a bracket 46 located immediately rearward of the flap 42 at the top of the frame 32. The snap switch 45 is mounted such that a motion is required in the desired direction of air flow in order to close its moveable contact. An extension forming a lever arm and denoted 47 is connected to the moveable contact of the snap switch 45, and the lever 47 extends down toward the trough 44 and engages the back of the flap 42. When the flap 42 takes its normal (i.e. absent the flow of combustion air) vertical disposition, the lever 47 engages the back of the flap 42, but the moveable contact of the snap switch 45 is still in an open position. When the motor 36 is energized to drive the propeller blade 38, the

air will be drawn in to force the flap 42. rearward thereby closing the contacts of the switch 45. The wires 48 signify the two wires to the snap switch 45; and they, too, are coupled to the connector 41 at the top of the frame 32.

Thus, the complete module containing the blower fan, flap and snap switch may be removed by disconnecting the connector 41, unscrewing screws holding the frame 32 to the furnace, and sliding the module out through the front, after having removed the lower vent and baffle plate 17.

System operation Turning now to FIG. 4, the operation of the air proving and draft booster system will now be described. An on/ off selection switch, schematically illustrated at 49, receives at one of its fixed terminals a lead from a conventional 12 volt storage battery 50. At another of its fixed terminals the selection switch 49 receives the output of a conventional voltage converter 51 adapted to convert volt, 60 cycle alternating voltage to 12 volts DC. The converter 51 receives energy from a 60 cycle AC source 52, if available.

The wiper arm of the switch 49 may be set to receive either the energy from the storage battery 50 or from a conventional electrical outlet through the voltage converter 51. The 12 volt DC current is then fed through the movable blade of the switch 49 to energize the blower motor 36 (provided, of course, a thermostat which is not shown calls for heat) thereby rotating the fan 38 and forcing air through the combustion intake conduit. When the flap 42 moves toward the blower 36, the lever arm 47 of the snap switch 45 will be forced rearward to close the switch 45, and energy from the selection switch 49 will then also be fed through the snap switch 45 to the main gas solenoid 28, to feed fuel to the burner 27 where it i ignited by a pilot light (not shown).

Hence, it is apparent that a reliable, fail-safe combustion air proving system is provided for generating a signal only when it has clearly been established that combustion air is flowing through the intake conduit before the main gas solenoid is turned on. Further, the particular vent and baffle arrangements prevent rain from entering the combustion air conduits. Any pressure differential between the outside of the flap 42 and the intake combustion air conduit is equalized by providing communication through the intake air conduit, the burner area, the outlet combustion air conduit and upper vent and battle plate 16.

Having thus described a particular embodiment of my invention, it will be obvious to persons skilled in the art that certain equivalent structures may be substituted for those described; and it is therefore intended that all such substitutions and modifications be covered as they are embraced within the spirit and scope of the appended claims.

I claim:

1. In a furnace system adapted for installation in an outside wall confining a space to be heated, the combination comprising: a front mounting panel for mounting flush with the exterior surface of said wall and defining a combustion air intake and exhaust apertures; combustion air channel means coupling said intake aperture with said exhaust aperture; a burner in said combustion air channel; a-ctuatable valve means normally inhibiting the flow of fuel to said burner; fan means in said combustion air channel adjacent said intake aperture; a flap pendantly mounted in said channel between said intake aperture and said fan means; and switch means for actuating said valve means in response to movement of said flap caused by the flow of air through said intake orifice.

2. The structure of claim 1 wherein said switch means comprises: a snap switch mounted in said channel immediately downwind of said flap and having a movable contact; and a lever arm extension coupled to said movable contact at one end and engaging said flap at the other, whereby said snap switch is sensitive to slight downwind movement of said flap.

3. The structure of claim 2 wherein said flap is characterized by extending perpendicular to the direction of air flow and substantially conforms to the interior contour of said channel adjacent said flap.

4. The structure of claim 3 further comprising U shaped bumper means in said channel beneath said flap and including upstanding leg members on either side of said flap for limiting movement thereof.

5. The structure of claim 1 further comprising a vent and bafile plate mounted on said front panel for preventing rain from entering said intake aperture while allowing air to be drawn therethrough.

6. The structure of claim 5 further comprising a second vent and baffle plate mounted on said front panel for preventing rain from entering said exhaust aperture, each of said vent and bafile plates including a solid plate directly in front of its associated aperture in spaced relation thereto, and a louvered portion adjacent to said plate and communicating with said associated aperture.

References Cited UNITED STATES PATENTS 2,790,868 4/1957 McClary 158-422 3,051,161 8/1962 Hicks 126-110 3,315,657 4/1967 Jensen et a1. l26-110 JAMES W. WESTHAVER, Primary Examiner.

M. Fletcher, Jr.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,394,696 July 30, 1968 Robert R. Cooper It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 4, after "said" insert solid Signed and sealed this 30th day of December 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR

fleeting Officer Commissioner of Patents 

